Tom Gruber on Tag Identity

Tom Gruber is famous for his striking and sensible aphorisms about ontologies such as "Every Ontology is a Treaty". He strikes again with this paper proposing an Ontology of Folksonomy.
In section 5, just before the conclusion, a bunch of questions about Tag Identity, showing that both Tags and URIs meet similar identification issues, in fact common to any naming mechanism, and neither is providing killing answers.